1. Field of the Invention
The present invention relates to a liquid crystal display device (LCD), and more particularly, to a liquid crystal display device having common-auxiliary electrodes surrounding pixel region and storage electrode in the pixel region.
2. Description of the Related Art
Recently, an LCD has been proposed where the liquid crystal is not aligned and the liquid crystal is driven by side electrodes insulated from pixel electrodes. FIGS. 1a and 1b are sectional views of pixel unit of the conventional LCDs.
Regarding conventional LCDs, a plurality of gate bus lines arranged in a first direction on a first substrate and a plurality of data bus lines arranged in a second direction on the first substrate divide the first substrate into a plurality of pixel regions.
A thin film transistor (TFT) applies image signal delivered from the data bus line to a pixel electrode 13 on a passivation layer 37. The TFT is formed on each pixel region and comprises a gate electrode, a gate insulator, a semiconductor layer, a source electrode, and a drain electrode, etc.
Pixel electrode 13 is formed on the gate insulator, thereon passivation layer 37 is formed over the whole first substrate, and side electrode 21 is formed surrounding the pixel electrode 13 and a part of pixel electrode 13 overlaps side electrode 21. (FIG. 1A)
Alternatively, pixel electrode 13 is formed on the gate insulator, and passivation layer 37 is formed over the whole first substrate.
On second substrate, a light shielding layer is formed to shield any light leakage from gate and data bus lines, and the TFT, a color filter layer is formed on the light shielding layer, an over coat layer is formed on the color filter layer, a common electrode 17 is formed to have open area 27 on the over coat layer, and a liquid crystal layer is formed between the first and second substrates.
The common electrode 17 is formed and applies electric field to a liquid crystal layer together with pixel electrode 13. Side electrode 21 and open area (slit) 27 distort the electric field applied to the liquid crystal layer.
Then, in a unit pixel liquid crystal molecules are driven variously. This means that when voltage is applied to the LCD, dielectric energy due to the distorted electric field arranges the liquid crystal directors in needed or desired positions.
In the LCDs, however, open area 27 in common electrode 17 or pixel electrode 13 is necessary, and the liquid crystal molecules could be driven stably when the open area is wider. If the electrodes do not have an open area or the width of the open area is narrow, the electric field distortion needed to divide the pixel region becomes weak. Then, when voltage over a threshold voltage, Vth, is applied, the time needed to stabilize the liquid crystal directors increases.
At this time, disclination occurs from the area where the liquid crystal directors are parallel with a transmittance axis of the polarizer, which results in a decrease in brightness. Further, according to the surface state of LCDs, the liquid crystal texture has an irregular structure.